Devices having bonded conductive and insulating substrates are fabricated with many different materials. A combination of metal, glass, and semiconductor materials are often used to create these devices and their packages. These materials are fused into a structure by many different processes as are known in the art. Some of these devices require a sealed chamber with a device therein and electrical connections to outside the package. Devices that typically have a requirement for this type of structure include all types of miniaturized switches or sensors, such as a pressure sensor for Tire Pressure Monitoring Systems (TPMS) for example. Considering the micromachined variety of switches and sensors, one feature many of these devices have in common is complex structures that must be contained in separate hermetic packaging, which can be difficult to manufacture and expensive to produce. In addition to packaging issues, there are operational issues.
Federal regulations are involved with Tire Pressure Monitoring Systems (TPMS). Therefore, reliability is an issue. In addition, Original Equipment Manufacturers (OEMs) have their own specifications for operation of TPMS. For example, having a tire pressure sensor in each tire of a vehicle that communicates to the vehicle over radio frequencies can cause confusion in situations where vehicles are in close proximity to each other such as parking lots. Further, tire pressure monitors are typically battery powered. Therefore, OEMs want a TPMS that only operates at particular time, so as to not crowd the airwaves and save battery power.
One solution is to provide a pressure sensor in a tire that includes an RF transmitter an RF receiver. The RF receiver of the sensor is used by the vehicle to tell the TMPS when to turn on and operate. However, the added RF receiver adds cost, and the sensor must periodically power the receiver to determine if a signal is being sent by the vehicle. Therefore, additional logic and clocking is required to provide this function. As a result, this solution adds costly circuitry and does not provide optimal battery usage.
Accordingly, there is a need for a tire pressure monitor system that is only operational when needed. It would also be of benefit, if the system could be provided in a simple assembly at a low cost and with a high reliability.